(A) new 3D diffuser lithography and its applications

Abstract

In this thesis, a new 3D diffuser lithography has been introduced. The 3D diffuser lithography technology gives a new way to form various rounded structures with excellent uniformity and reproducibility. The 3D diffuser lithography is compatible with the conventional lithography technology. The only difference between them is the use of a diffuser on a photomask. Since the diffuser randomizes the direction of the UV light, the exposed region forms a circular or an elliptical cross-section after development process. Various cross-sectional photoresist profiles were obtained by changing kind of diffusers, UV exposure dose, and pattern width. Furthermore, quite dense patterns having sharp borders could be obtained by over-exposing UV light through the diffuser and the mask with very close open patterns. This method will greatly simplify fabricating the 3D microstructures with the rounded-shape, enabling various new 3D microstructures and applications. First, by using the 3D diffuser lithography and PDMS replication method, surface and 3D planar microlenses were simply fabricated. The fabricated surface microlenses had focal lengths of from 10 um to 15 um with the different heights. They showed a focal spot which had almost the same diameter as that of the ideal spherical shape. The proposed method for the microlens fabrication has three major advantages over conventional methods. First, the process is very simple. Second, the microlens shape can be controlled precisely and reproducibly by changing the process parameters of the 3D diffuser lithography. Finally, the microlens array with a fill-factor of almost 100% could be fabricated in a lithographical way, which was difficult to achieve with conventional technologies. Also, a new 3D planar microlens which had excellent light focusing characteristics and facility in monolithic integration was proposed and fabricated by help of the 3D diffuser lithography. Its focal length (350 um) and focal spot (4.0 um in ...